从八度结构中提取给定字段名的所有行的值 [英] Extract values for all row, for given fieldname, from an Octave struct

问题描述

如何从八度 struct 的所有行中获取完整列(字段名)的所有值?

How can I get all values of a complete column (fieldname), for all rows, from an Octave struct?

我最好将其放入单元格数组或常规向量中，最好不要循环.

I would get it into a cell array, or a regular vector, preferably without looping.

推荐答案

您似乎有些困惑.部分原因是您将结构与"R dataframes/python pandas"进行等价比较.

You seem to be confusing a few things. Partly because of your equivalence comparison of structs to "R dataframes / python pandas".

最好将结构与python字典，R列表等类似.它们是一个特殊的对象，可以容纳字段"，可以通过字段名"(或键访问的值，如果您访问)更喜欢).

Structs are better thought of as being similar to python dicts, R lists, etc. They are a special object that can hold 'fields', which can be accessed by a 'fieldname' ( or values accessed by keys, if you prefer ).

同样，与八度中的任何其他对象一样，它们也是数组的有效元素.这意味着您可以拥有这样的东西:

Also, like any other object in octave, they are valid elements for an array. This means you can have something like this:

octave:1> struct( 'name', { 'Tom', 'Jim'; 'Ann', 'Sue' }, 'age', { 20, 21; 22, 23 } )
S =
  2x2 struct array containing the fields:
    name
    age

通常，当一个人处理这样的结构 array 时，访问数组中多个元素上的字段会产生

In general, when one deals with such a struct array, accessing a field on more than one elements of the array, produces a comma separated list. E.g.

octave:6> S(2,:).name
ans = Ann
ans = Sue

此函数可以传递给(例如扩展为")任何期望以逗号分隔的列表作为参数的函数.例如

This can be passed to (i.e. "expanded into") any function that expects such a comma separated list as arguments. E.g.

octave:7> fprintf( 'The girls names are %s, and %s.\n', S(2,:).name )
The girls names are Ann, and Sue.

如果需要，还可以将该列表直接传递到单元构造器"中，以创建单元.(尽管如果您希望它具有特定的形状，则必须在后缀后重塑它的形状).例如

If you want, you can also pass that list straight into a 'cell constructor', to create a cell. (though if you want it to have a particular shape, you'll have to reshape it afterwords). E.g.

octave:9> reshape( { S.age }, size(S) )
ans =
{
  [1,1] =  20
  [2,1] =  22
  [1,2] =  21
  [2,2] =  23
}

也有 struct2cell ，但这有所不同.尝试一下以查看其作用(例如 C = struct2cell(S)).

There is also struct2cell but this does something different. Try it to see what it does (e.g. C = struct2cell(S) ).

最后，为避免混淆，考虑到当处理结构数组时，列"是指数组"中的列，因此，我将避免使用该术语指代字段名".

Finally, to avoid confusion, given the fact that when one deals with struct arrays, "columns" refer to columns in the 'array', I would avoid referring to "fieldnames" by that term.

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